Abstract

We survey the fundamental problems of designing general purpose, descriptive query languages for object-oriented database systems. Structural aspects of object models are investigated and their implications on the query language capabilities are analyzed and summarized as requirements that should be met by a `good' object-oriented query language. The type system of an OODB model has to distinguish atomic types (such as basic data types -- numbers, strings, -- or abstract object types) and constructed types (such as sets and tuples). Each of the type constructors should be supported by an adequate set of generic access and manipulation operators. The query language should allow orthogonal combination of operators according to the nesting structure of type constructors, the model should be closed against its operators, and the language should be adequate. The latter criterion ensures, for instance, that queries can be expressed that return objects instead of just data about objects ("object preservation"). Several recent proposals for query languages are evaluated against these criteria.

Citations